An atomic version of the Millikan oil drop experiment is performed computationally. It is shown that for planar molecules, the atomic version of the Millikan experiment can be used to define an atomic partial charge that is free from charge flow contributions. We refer to this charge as the Millikan-Thomson (MT) charge. Since the MT charge is directly proportional to the atomic forces under a uniform electric field, it is the most relevant charge for force field developments. The MT charge shows good stability with respect to different choices of the basis set. In addition, the MT charge can be easily calculated even at post-Hartree-Fock levels of theory. With the MT charge, it is shown that for a planar water dimer, the charge transfer from the proton acceptor to the proton donor is about −0.052 e. While both planar hydrated cations and anions show signs of charge transfer, anions show a much more significant charge transfer to the hydration water than the corresponding cations. It might be important to explicitly model the ion charge transfer to water in a force field at least for the anions.

中文翻译：

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在分子尺度上进行Millikan实验：通过计算测量原子力确定原子Millikan-Thomson电荷

Millikan油滴实验的原子形式是通过计算执行的。结果表明，对于平面分子，可以使用Millikan实验的原子形式来定义没有电荷流贡献的原子部分电荷。我们将此费用称为密立根-汤姆森（MT）费用。由于MT电荷在均匀电场下与原子力成正比，因此它是与力场发展最相关的电荷。MT电荷对于基础集的不同选择显示出良好的稳定性。此外，即使在Hartree-Fock后理论水平上，也可以轻松计算MT费用。对于MT电荷，显示出对于平面水二聚体，电荷从质子受体向质子供体的转移为约-0.052e 。虽然平面水合阳离子和阴离子都显示出电荷转移的迹象，但阴离子显示出比相应阳离子显着得多的电荷转移到水合水中。显式地模拟至少在阴离子中在力场中离子电荷转移到水中的过程可能很重要。